Abstract

One of the 12 principles of Green Chemistry is the use of catalysts in preference to stoichiometric reagents to enhance the atom economy and yield of chemical reactions. Oxidation of alcohols to the corresponding carbonyl compounds is an industrially important reaction as it yields useful by products.

Environmentally hazardous metal ions like Cr(VI), Os(VIII) and Ru in different oxidation states have been routinely used to catalyse the oxidation of alcohols. As a green initiative, we have used the relatively inexpensive and less harmful transition metal ions to catalyse the oxidation of alcohols used in the manufacture of perfumes and fragrances.

This paper reports the kinetic study of the oxidation of the unsaturated primary perfumery alcohol, Cinnamyl alcohol by Ce(IV) in acidic medium. The oxidation was carried out under first order kinetic conditions with respect to Ce(IV) at different temperatures. From the variation of oxidation rate with temperature, the thermodynamic activation parameters of the reaction were evaluated and correlated with the proposed reaction mechanism. The effect of ionic strength on the oxidation was studied in dilute solution using Analar Grade K₂SO₄.

Transition metal ions Mn(II),Co(II),Ni(II),Cu(II) and Zn(II) in the concentration range [M(II)]=2.5 -5.0 x 10-4mol dm-3 were used to catalyse the oxidation of Cinnamyl alcohol by Ce(IV) in acidic medium and the sequence of their catalytic efficiencies was determined as Mn(II)>Co(II)>Ni(II)>Cu(II)>Zn(II).Mn(II) ions seem to be the best catalysts among the transition metal ions studied. Suitable reaction mechanisms have been proposed for the oxidation of Cinnamyl alcohol in the presence and absence of transition metal ion catalysts.

Keywords:Cinnamyl alcohol; Oxidation; Ce (IV); Kinetics; Transition metal ion catalysts; Catalytic efficiency; Hyper valent ions; Ionic strength; Thermodynamic activation parameters; Reaction mechanism